Structural and magnetic properties of Co₆₅C₃₅ nanocomposite films prepared by pulsed filtered vacuum arc deposition

In this paper, the Co₆₅C₃₅ nanocomposite film was prepared by pulsed filtered vacuum arc deposition. Subsequent thermal annealing was performed in a vacuum furnace (~ 8 × 10^-4 Pa) at various temperatures. The films were characterized by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and magnetic force microscopy (MFM). The magnetic properties were measured by a SQUID magnetometer. The as-deposited film was found to be amorphous and soft ferromagnets. No obvious magnetic domain structures can be observed in the MFM image, indicating the low anisotropy in the amorphous film. After annealing at a temperature between about 300°C and 350°C, the as-deposited amorphous films went through a meta-stable stage at which a cobalt carbide phase and hexagonal close-packed (hcp) crystalline cobalt co-existed. Upon increasing of annealing temperature to 400°C, the carbide phase decomposed into hcp crystalline cobalt nanograins and graphite-like carbon. Clear MFM images with obvious long-range magnetic structures can be obtained in the annealed films. The strengthened MFM images contrast implied the enhanced magneto-crystalline anisotropy owing to the nanocrystallization of Co grains within the films. The magnetic hardening was demonstrated by the round-shaped magnetic hysteresis loops.